Fillée Catherine, Cumps Jean, Ketelslegers Jean-Marie
Cliniques Universitaires St-Luc, Université Catholique de Louvain, Brussels, Belgium.
Clin Lab. 2012;58(7-8):725-36.
Free T4 (FT4) and free T3 (FT3) immunoassays exhibit wide inter-assay variations. We therefore established control values with three different immunoassays and compared their clinical performances in thyroidal diseases and severe/acute non-thyroidal illnesses (NTI).
The UniCel DxI 800, Architect i2000, and Elecsys 2010 assays were used. FT4 and FT3 reference ranges were established in 68 controls, without conditions interfering with thyroid function, with normal TSH (0.35-3.02 mU/L) and negative anti-thyroid peroxidase antibodies. Free hormones were determined in 60 patients with thyroid diseases (TSH: < 0.001-31.5 mU/L) and 45 NTI patients (TSH: 0.10-4.72 mU/L). Control values were normalized as Z-scores; patients' results were expressed as Z-scores, using the control values of each assay. Pairwise comparisons of the Z-scores were performed by Deming's regression. Classification of patients' results based on 95% control values were evaluated by kappa agreement statistics.
Control values for FT4 (pmol/L; geometrical means; 95% confidence intervals) were: 11.1 (7.6-16.1), 12.3 (9.1-16.6), 15.6 (11.4-21.4) and for FT3: 4.8 (4.0-5.7), 4.0 (3.0-5.3), 4.3 (3.1-5.09), with DxI 800, Architect, and Elecsys, respectively. Pairs of control Z-scores correlated significantly, but with different strengths (FT4: r = 0.915, 0.740, 0.770; FT3: r = 0.615; 0.589; 0.790, for DxI 800 vs. Elecsys; DxI 800 vs. Architect; Elecsys vs. Architect; p < 0.001); slopes and intercepts of paired controls were 1.00 and zero. In thyroid diseases, slopes of FT4 Z-scores among assays differed slightly from 1.00 (1.11, 0.88, 0.87 for DxI versus Elecsys, DxI 800 versus Architect, Elecsys versus Architect, respectively; p < 0.05); slopes of FT3 Z-scores were consistent with unity, except for DxI 800 versus Elecsys (0.88; p < 0.05). In NTI patients, regression slopes were consistent with unity (p < 0.05). The agreement statistics showed moderate to very good inter-assay concordances for thyroid and NTI patients' results.
FT4 and FT3 assays show moderate to very good agreement, in patients with thyroid diseases or NTI when compared pairwise to their control values. Slight quantitative differences between some pairs of assays are observed in thyroid diseases, after normalization as Z-scores.
游离甲状腺素（FT4）和游离三碘甲状腺原氨酸（FT3）免疫测定法显示出较大的批间差异。因此，我们使用三种不同的免疫测定法建立了对照值，并比较了它们在甲状腺疾病和严重/急性非甲状腺疾病（NTI）中的临床性能。
使用UniCel DxI 800、Architect i2000和Elecsys 2010测定法。在68名对照者中建立FT4和FT3参考范围，这些对照者没有干扰甲状腺功能的情况，促甲状腺激素（TSH）正常（0.35 - 3.02 mU/L）且抗甲状腺过氧化物酶抗体阴性。对60例甲状腺疾病患者（TSH：< 0.001 - 31.5 mU/L）和45例NTI患者（TSH：0.10 - 4.72 mU/L）测定游离激素。对照值标准化为Z分数；患者结果以Z分数表示，使用每种测定法的对照值。通过戴明回归进行Z分数的成对比较。基于95%对照值对患者结果进行分类，并通过kappa一致性统计进行评估。
FT4（pmol/L；几何均值；95%置信区间）的对照值分别为：使用DxI 800时为11.1（7.6 - 16.1），使用Architect时为12.3（9.1 - 16.6），使用Elecsys时为15.6（11.4 - 21.4）；FT3的对照值分别为：使用DxI 800时为4.8（4.0 - 5.7），使用Architect时为4.0（3.0 - 5.3），使用Elecsys时为4.3（3.1 - 5.09）。成对的对照Z分数显著相关，但强度不同（FT4：DxI 800与Elecsys相比，r = 0.915、0.740、0.770；DxI 800与Architect相比，r = 0.740、0.589、0.790；Elecsys与Architect相比，r = 0.770、0.589、0.790；p < 0.001）；成对对照的斜率和截距分别为1.00和零。在甲状腺疾病中，各测定法之间FT4 Z分数的斜率与1.00略有不同（DxI与Elecsys相比为1.11，DxI 800与Architect相比为0.88，Elecsys与Architect相比为0.87；p < 0.05）；FT3 Z分数的斜率除DxI 800与Elecsys相比外（0.88；p < 0.05）均与1一致。在NTI患者中，回归斜率与1一致（p < 0.05）。一致性统计显示，甲状腺疾病和NTI患者结果的批间一致性为中等至非常好。
与对照值进行成对比较时，FT4和FT3测定法在甲状腺疾病或NTI患者中显示出中等至非常好的一致性。在标准化为Z分数后，在甲状腺疾病中观察到某些成对测定法之间存在轻微的定量差异。
